Process for producing conjugated dienes

ABSTRACT

Large surface area oxidative dehydrogenation catalysts which are suitable for converting C 4  to C 8  mono-olefins to conjugated dienes are disclosed, comprising the oxides of vanadium, phosphorus, tin and potassium in combination with hydrogen mordenite having a surface area between 30 M 2  /g to 450 M 2  /g and wherein the vanadium has an average valence in the range of from 3.5 to 4.95.

This application is a division, of application Ser. No. 328,446, filed Dec. 7, 1981 now U.S. Pat. No. 4,454,245.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to oxidative dehydrogenation catalysts, and more particularly to mordenite oxidative dehydrogenation catalysts which are useful for producing diolefins from C₄ to C₈ mono-olefins.

2. The Prior Art

The use of dehydrogenation catalysts to oxidize hydrocarbons to diolefins is known and appreciated by the prior art. For example, U.S. Pat. No. 3,927,138 relates to a process for producing diolefins from paraffins, especially the dehydrogenation of butane to butenes and butadiene, using an oxidation catalyst consisting of a ferrous metal, tin, phosphorus and an alkali metal. The catalysts may be supported on or diluted with materials such as silica, alumina, boria, etc.

U.S. Pat. No. 3,914,332 discloses a process for the oxidative dehydrogenation of butane to a mixture of butenes and butadiene using a vanadium-potassium-sulfur catalyst supported on silica, which permits the use of high space velocities.

U.S. Pat. No. 3,856,881 relates to a process for the dehydrogenation of C₄ to C₅ hydrocarbons to produce the corresponding dehydrogenated compounds. The dehydrogenation catalyst used consists of a crystalline spinel of a phosphorus and divalent-metallic vanadium compound. Catalyst carriers such as alumina, pumice, silicon, etc. are additionally described as suitable for use in the dehydrogenation catalyst.

U.S. Pat. No. 3,789,078 discloses a dehydrogenation process and dehydrogenation catalysts which are useful for oxidatively dehydrogenating organic compounds such as alkenes, alkadienes, cycloalkenes, alkylpyridines and alkyl aromatics. The catalyst consists of a combination of phosphorus, tin and a Group IA or IIA metal of the Periodic Table. Substantially any phosphorus, tin and Group IA or IIA containing materials may be employed in the catalyst so long as at least one of the materials used contains oxygen.

U.S. Pat. No. 3,775,508 relates to an oxidative dehydrogenation process for dehydrogenating C₂ to C₁₀ alkenes, alkadienes, etc. using an oxidation catalyst consisting of phosphorus, tin and a Group IA or IIA metal of the Periodic Table. The catalyst is improved by including a heat-volatile activity-stimulating ammonium salt in the catalyst composition prior to the catalyst particle-forming stage.

As can readily be determined from the above, there is an ongoing effort to develop oxidative dehydrogenation catalysts for producing diolefins from alkanes and olefins.

Accordingly, it is an object of the present invention to provide an oxidative dehydrogenation catalyst for producing diolefins from mono-olefins.

Another object of the present invention is to provide an oxidative dehydrogenation catalyst having a large surface area which is useful for producing butadiene and to provide a method of preparing the same.

A further object of the present invention is to provide a method for obtaining improved yields and selectivity of olefins, for example, butadiene.

These and other objects are accomplished according to the present invention by oxidizing a C₄ to C₈ mono-olefin to the corresponding diolefin in the presence of an alkali metal promoted oxidative dehydrogenation catalyst comprising the oxides of vanadium, phosphorous and tin on a hydrogen mordenite support.

SUMMARY OF THE INVENTION

The present invention resides in a dehydrogenation catalyst described by the formula:

    Me.sub.a V.sub.b P.sub.c Sn.sub.d O.sub.e X

wherein X is hydrogen mordenite, Me is an alkali metal, a is 0.10 to 2, b is 0.10 to 1, c is 1, d is 0.001 to 0.30 and e is a number which satisfies the valence requirements of the other elements present.

The invention additionally resides in a method of preparing an alkali metal promoted, vanadium, phosphorus, tin, mixed-oxide, mordenite, oxidative dehydrogenation catalyst which comprises:

(A) reacting an alkali metal containing compound, a vanadium compound and a phosphorus compound in an acidic aqueous solution with a tin compound under reaction conditions which will provide vanadium having an averae oxidation state of 3.50 to 4.95 to form a catalyst precursor,

(B) admixing the catalyst precursor with a binder, solvent and mordenite to form an impregnated mordenite, and

(C) calcining the oxidation catalyst at temperatures in the range of from 400° F. to 1,200° F., for 1/2 hour to 6 hours.

A method for producing diolefins or conjugated dienes is disclosed which comprises reacting a C₄ to C₈ mono-olefin with a gas containing helium and molecular oxygen in the vapor phase, under reaction conditions and in the presence of a dehydrogenation catalyst described by the formula:

    Me.sub.a V.sub.b P.sub.c Sn.sub.d O.sub.e X

wherein X is mordenite, Me is an alkali metal, a is 0.10 to 2, b is 0.10 to 1, c is 1, d is 0.001 to 0.30, and e is a number which satisfies the valence requirements of the other elements present.

DETAILED DESCRIPTION OF THE INVENTION

Broadly described, the catalysts of this invention have the general formula:

    Me.sub.a V.sub.b P.sub.c Sn.sub.d O.sub.e X

wherein X is mordenite, Me is an alkali metal, a is 0.10 to 2, b is from 0.10 to 1, c is 1, and d is from 0.001 to 0.30. The above formula is not an empirical formula, however, the numbers assigned to the subscript letters, i.e., a, b, c and d represent the atomic ratio of the respective Me, V, P and Sn active components of the catalyst. The e in the above formula may vary widely depending on the mixed oxide combination within the catalyst complex. The only restriction of the e value is that the number assigned to e must satisfy the valency requirements of the other elements in the catalyst complex.

Generally, oxygen combines with the alkali metal, vanadium, phosphorus and tin to form a catalyst precursor which is an oxygen complex or the oxides of these compounds. The oxygen content of the catalyst precursor will vary depending upon the relative stoichiometry of the potassium, vanadium, phosphorus and tin present. However, e will normally have a value of from 2 to 12, preferably from 2.5 to 8.

One disadvantage of using acidic catalysts to produce diolefins from mono-olefins is that basic products have a tendency to remain on the catalyst surface and react further. Thus, a reaction to produce diolefins from mono-olefins and alkanes would, under these circumstances proceed to a more acid product, for example, maleic anhydride from butene or butane. This problem is solved by the addition of an alkali metal promoter to the acidic dehydrogenation catalyst to render said catalyst less acidic. Although the invention is not limited to any basic theory, it is believed that a basic product or molecule, for example, 1,3 butadiene when butene is the feed source, will desorb from said catalyst rather than remain on the catalyst surface to react further and produce an acidic product or compound. This concept may be further described by the fact that the energy required to remove an electron (the ionization potential) from a basic molecule is smaller than the energy similarly required from an acid molecule. Selective oxidation reactions can therefore be classified into various types, depending on the ionization potential of the hydrocarbon reaction and of the hydrocarbon product. For example, the reaction of butene to butadiene may be classified as a basic to basic type reaction, while the reaction of butadiene to maleic anhydride may be classified as a basic to acidic type reaction. For the basic to basic or mono-olefin to diolefin reaction to proceed, there must be cooperative action between both acidic and basic sites on the catalyst. For example, basic reactant molecules are dissociatively adsorbed on acidic sites which extract a hydrogen atom as H⁻ and thus generate an allyl radical. The radical moves to a neighboring basic site where it loses a second hydrogen and is partially oxidized to the resulting basic product. The product, being basic, easily desorbs from the basic site. Oxygen near the basic site is replaced by an oxygen of the catalyst lattice which is near an acidic site, and the oxygen of the gaseous phase replenishes the latter. Thus, good selectivities for reactions of the basic to basic type need both acidic and basic sites on the catalyst surface.

Alkali metals which are suitable as promoters herein include lithium, sodium, potassium, rubidium and cesium. The preferred alkali metal is potassium. Suitable alkali metal compounds useful as a source of alkali metals are selected from alkali metal salts such as the phosphates, i.e., meta, ortho, pyro, tri etc., the carbonates, chlorides, oxalates and acetates. An especially desirable alkali metal compound is potassium meta phosphate.

Vanadium compounds useful as a source of vanadium in the catalyst precursor are those vanadium compounds known to the art. Suitable vanadium compounds include vanadium salts, such as ammonium metavandate and vanadyl sulfate; vanadium oxides, such as vanadium pentoxide; and vanadium oxyhalides, such as vanadium oxytrichloride. However, pentavelent vanadium compounds such as ammonium metavanadate and vanadium pentoxide are preferred.

Phosphorus compounds useful as a source of phosphorus in the catalyst precursor are also those known to the art. Suitable phosphorus compounds are selected from phosphoric acid, phosphorus pentoxide, ammonium phosphate and diammonium phosphate. The preferred phosphorus compounds are pentavelent phosphorus compounds such as phosphoric acid and phosphorus pentoxide.

Suitable tin compounds are those tin compounds which have a valence of +2, since the tin compound acts as a reducing agent for the vanadium compound in the catalyst. Tin compounds useful herein preferably are selected from stannous chloride, stannus fluoride, stannous bromide, stannous oxide, stannus sulfate, stannous acetate, stannous pyrophosphate, and stannous oxalate. Upon reaction of the tin compound with the vanadium compound, tin +2 (stannous) will be oxidized up to the tin +4 (stannic) oxidation state and vanadium in the +5 oxidation state will be reduced to an average oxidation state of less than +5.

The catalyst precursor is preferably produced by dissolving and mixing compounds containing an alkali metal, vanadium, phosphorus and tin in an acidic-aqueous medium such as water and hydrochloric acid, hydroiodic acid, hydroformic acid, acetic acid, oxalic acid, maleic acid, citric acid or formic acid. The alkali metal-vanadium-phosphorus-tin compounds are contacted at an atomic ratio of alkali metal-vanadium-phosphorus-tin of from 0.10:0.10:1:0001 to 2:1:1:0.30, preferably from 0.4:0.20:1:0.002 to 1-:1:1:0.20. The atom ratio of vanadium to phosphorus in the starting material is important since it controls the vanadium to phosphorus atom ratio in the final catalyst. When the oxidation catalysts herein contain a vanadium-phosphorus atom ratio below 0.10:1 or above 1.00, the yield of diolefin using these catalysts is so low as to render the reaction commercially unattractive. It should be noted that phosphorus aids in stabilizing vanadium in the final catalyst composition, the alkali metal compound renders the catalyst surface basic which favors production of diolefins from mono-olefins, while tin +2 acts as a reducing agent which aids in the reduction of vanadium to a valance state of less than +5. It should additionally be noted that the above-described acids which dissolve the alkali metal, vanadium, phosphorus and tin compounds act as reducing agents for the vanadium compounds. However, the reduction process takes from one-half hour to about one hour when tin is not present in the reaction medium. Upon the addition of tin to the reaction medium, the reduction of vanadium to a valence of less than +5 takes place almost instantly, i.e., less than one minute. Generally, the vanadium is reduced to an average valence within the range of from +3.50 to +4.95, preferably from +4.10 to +4.70.

Conventional apparatus and techniques known to the art may be used to dissolve and react the components which make up the catalyst precursor. For example, temperatures of from 100° F. to 220° F., preferably from 180° F. to 220° F. and a reaction time of from 1/2 hour to 6 hours under atmospheric pressure normally are sufficient to dissolve and react the alkali metal, vanadium, phosphorus and tin compounds. However, pressures from atmospheric pressure to 50 p.s.i.g. may be used to shorten the dissolution and reaction times. Generally, agitation is supplied during the reaction period to ensure complete contact of the reactants. Agitation is defined herein as mixing, rocking, shaking, etc.

After the reaction proceeds to completion the catalyst precursor is concentrated and collected using conventional methods and techniques and admixed with a zeolite of the mordenite crystal structure to form an impregnated mordenite.

The crystalline aluminosilicate employed in this invention is a zeolite of the mordenite crystal structure, which is highly siliceous in nature and is generally characterized by a silica-alumina mole ratio range of from about 6 to about 20 as found in nature. The mordenite crystal lattice comprises as the basic building block a tetrahedron consisting of one silicon or aluminum atom surrounded by four oxygen atoms. Each tetrahedron belongs to one or more four and five membered rings in the framework. The high degree of thermal stability of mordenite is probably due to the large number of five membered rings which are energetically favored in terms of stability.

Rings of twelve tetrahedra from pores or channels running parallel to the crystal axis of mordenite to give a tubular configuration. This structure is unique among the aluminosilicates or zeolites, because the channels or tubes do not intersect, and access to the cages or cavities is in one direction only. For this reason mordenite is referred to as two-dimensional. Other well known zeolites, for example, faujasite, etc. contain twelve membered rings of tetrahedra, but they have interconnected cages which allow access from three directions.

Commercially available mordenites are typically prepared by heating an alkali metal aluminate in solution with an alkali metal hydroxide in contact with a silica source such as sodium silicate, reactive amorphous silica gel, or aqueous colloidal silica sol, at a temperature of about 180° to 200° F. Crystallization occurs over a relatively short period of time, for example, eight to twelve hours. The hydrogen form of mordenite is prepared by acid extraction of sodium mordenite with relatively strong mineral acids, for example hydrochloric acid, nitric acid, etc. Synthetic mordenite prepared in accordance with the above described procedure is available commercially from the Norton Company under the tradename of Zeolon.

The mordenite provides not only the required surface of the catalyst precursor, but gives physical strength and stability to the catalyst material. In addition, the mordenite has a large surface area upon which the catalyst precursor is deposited.

Generally, from 15 to 50 weight percent of the catalyst precursor comprising the oxides of an alkali metal vanadium, phosphorus and tin, is mixed with from 50 to 85 weight percent of the mordenite. Binding agents and additives may optionally be added to the catalyst to provide the proper consistency of the catalyst prior to mixing and forming said catalyst. The binding agents and additives, when used, preferably comprise from 0.1 to 10, especially from 3 to 10 weight percent of the finished catalyst. Suitable agents include methyl cellulose, silica, and alumina. Additives suitable for use herein include organic polar solvents such as ethanol, propanol, isopropanol, butanol, etc. The binding agents and additives are normally mixed in a weight ratio of from 1:20 to 20:1. The preferred method of mixing the catalyst precursor and mordenite is by comulling. However, other conventional mixing techniques may be used.

The physical form of the catalysts of this invention depends to a large extent upon the technique of drying and/or the desired shape. The catalysts may be produced as spheres, pellets, beads, elongated cylinders, and three-lobe or cloverleaf configurations. For example, the composites may be filtered and oven dried and course granules may be obtained by breaking up and sieving the oven-dried cake up to any desired size. Spray drying the catalyst, so that the dried catalyst will pass through a 4 to 200 mesh sieve (U.S.) is another method of producing the desired catalyst. Another method involves shapeboring the catalyst into a desired configuration using a restraint to maintain the desired shape and thereafter drying the catalyst. A particularly desirable shape is a cylindrical configuration having a diameter of from 1/16 inch to 1/8 inch and a length of from 1/4 inch to 1/2 inch.

The final catalyst is activated by calcination which preferably is performed in an air or oxygen atmosphere at a temperature of from about 400° F. to about 1,200° F., for about 1/4 hour to about 6 hours, preferably from about 1/2 hour to about 4 hours.

The catalyst thus produced is especially suited for oxidizing C₄ to C₈ mono-olefins to the corresponding diolefins and has a surface area of from 30 M² /g to 450 M² /g, a pore volume of from 0.1 cc/g to 0.8 cc/g and a compacted bulk density of from 0.35 to 1.50 g/cc.

A variety of reactors may be used in the oxidation reactions herein. For example, conventional fluidized bed reactors and fixed-bed or tube, heat exchanger type reactors are satisfactory; the details of the operation of such reactors as well known to those skilled in the art. The oxidation reaction is an exothermic reaction, necessitating relatively close control of the reaction temperature. It is desirable to have the surface of the reactor at a constant temperature and some medium may be necessary to conduct heat away from the reactor to aid temperature control. Examples of desirable media include molten sulfur, mercury, molten lead, or eutectic salt baths, for example a sodium nitrate-nitrate eutectic constant temperature mixture. An additional method of temperature control is the use a metal block reactor whereby the metal surrounding the reactor chamber acts as a temperature regulating body. Conventional heat exchangers may also be used.

Normally a reaction mixture of a gaseous feed stream comprising a C₄ to C₈ mono-olefin and a molecular oxygen containing gas, for example, air, a mixture of air and oxygen, mixtures of carbon dioxide and oxygen or mixtures of nitrogen or steam with air or oxygen is charged to a reaction zone, for example, a conventional pressure reactor. The gaseous feed stream generally will contain a molecular oxygen containing gas and from about 0.1 to about 5 mole percent, especially from about 0.1 to about 3 mole percent, especially from about 0.1 to about 2.5 mole percent of a C₄ to C₈ mono-olefin for optimum yield of the corresponding diolefins. Although higher concentrations of mono-olefin may be employed, they are not recommended because explosive hazards may be encountered. It should additionally be noted that the inert gas helium may be employed as a carrier in the process herein without deleterious effect upon the dehydrogenation reaction. Normally, the helium, molecular oxygen and C₄ to C₈ mono-olefin are introduced into a reactor at a molar ratio range of from 0.10:1:0.001 to 4:1:0.03, especially from 4:1:0.01 to 4:1:02.

Olefins which may be used to produce diolefins are selected from mono-olefins containing 4 to 8 carbon atoms. For example, desirable olefins include butene, pentene, cyclopentene, hexene, cyclohexene, heptene, cycloheptene, octene, or a mixture thereof.

Preferably the gaseous feed stream comprising molecular oxygen and a C₄ to C₈ mono-olefin is reacted in the presence of an oxidation catalyst described by the formula:

    Me.sub.a V.sub.b P.sub.c Sn.sub.d O.sub.e X

wherein X is mordenite, Me is an alkali metal, a is 0.1 to 2, b is 0.1 to 1, c is 1, d is 0.001 to 0.30 and e is a number which satisfies the valence requirements of the other elements present. The flow rate of the gaseous feed stream through the pressure reactor may be varied within rather wide limits but a preferred flow rate consists of a gas hourly space velocity (GHSV) of from 2,400 to 6,000 reciprocal hours.

The temperature of reaction may be varied herein, but normally the reaction should be conducted at temperatures within a rather critical range. The overall temperature range for the conversion of C₄ to C₈ mono-olefins to the corresponding diolefins preferably is from 500° F. to 760° F., especially from 600° F. to 700° F.

Typically, the reaction pressure is from atmospheric pressure to 200 p.s.i.g., preferably from atmospheric pressure to 50 p.s.i.g., as previously stated, the reaction may be carried out in any reactor suitable for effecting vapor-phase oxidation reactions, but preferably a fixed catalyst bed reactor is employed.

The invention is further illustrated by the following examples which are illustrative of various aspects of the invention and are not intended as limiting the scope of the invention as defined by the appended claims.

EXAMPLE I

A dehydrogenation catalyst having an average oxidation state of 4.72 for vanadium is prepared by charging 14.0 grams (0.12 moles) of ammonium metavandate, 1,8 grams (0.008 moles) of stannous chloride, 50 ml of distilled water, 10 ml of ethanol and 11 ml of concentrated hydrochloric acid to an 800 ml round bottom flask equipped with a water cooled condensor, heating mantle and magnetic stirrer. The above-described mixture turns green. Next, 18.0 grams (0.153 moles) of potassium metaphosphate, 15 ml of distilled water and 16.5 grams (0.198 moles) of 85 percent phosphoric acid are introduced into the flask. This mixture is heated to a temperature of 122° F. and agitated with a magnetic stirrer for 18 hours.

The non-homogeneous mixture is mixed with 8.0 grams of silica, 120 4.72 ms of H+ mordenite, air-dried at 230° F. for 12 hours, and then calcined in air at 930° F. for 2 hours. The resulting catalyst is screened to give an 80-100 mesh (U.S.) catalyst particle size. The catalyst has a surface area of 41 M² /g and a potassium-vanadium-phosphorus-tin atomic ratio of 0.44:0.34:1.0:0.023.

EXAMPLE II

A dehydrogenation catalyst having an average oxidation state of 4.62 for vanadium and a surface area of 226 M² /gram is prepared by charging 14.0 grams (0.120 mole) of ammonium metavanadate, 1.8 grams (0.008 mole) of stannous chloride, 50 ml of distilled water, 10 ml of ethanol and 11 ml of concentrated hydrochloric acid to an 800 ml round bottom flask equipped with a water cooled condensor, heating mantle and magnetic stirrer. Then 18 grams (0.152 mole) of potassium metaphosphate, 15 ml of distilled water and 16.5 grams (0.168 moles) of 85 percent phosphoric acid are introduced into the flask. The mixture is heated to a temperature of 122° F. and agitated with magnetic stirrer for 12 hours.

The dark green slurry produced above is co-mulled with 8.0 grams of silica and 120 grams of H+ mordenite using a model no. 472 Lancaster Mixer, manufactured by Posey Iron Works, Inc. of Lancaster, Pa. The mixture is operated at 36 RPM. The resulting slurry is calcined in air at 930° F. for 3 hours. The catalyst thus formed has a potassium-vanadium-phosphorus-tin atomic ratio of 0.47:0.31:1.0:0.024.

EXAMPLE III

A dehydrogenation catalyst having an average oxidation state of 4.74 for vanadium and a surface area of 142 M² /g is prepared in accordance with the procedure used in Example I with the following exceptions:

38.04 grams (0.280 mole) of potassium metaphosphate and 2.70 grams (0.280 mole) of phosphoric acid are utilized. The resulting catalyst has a potassium-vanadium-phosphorus-tin atomic ratio of 0.91:0.39:1.0:0:0.026.

EXAMPLE IV

A dehydrogenation catalyst having a surface area of 363 M² /g and an average oxidation rate of 4.83 for vanadium is prepared using the procedure described in Example II with the following exceptions:

3.3 grams (0.028 moles) of potassium metaphosphate and 27.4 grams (0.028 moles) of phosphoric acid are used. The catalyst has a potassium-vanadium-phosphorus-tin-ratio of 0.09:0.39:1.0:0.026.

EXAMPLE V

1,3 butadiene is produced from butene by charging 1 ml (0.40 grams) of the catalyst of Example II to a continuous flow catalytic reaction system equipped with programmable gas chromatograph and marketed commercially under the tradename Flow Diagram S Chematic-CDS 800 CF-HP/GC Catalytic Reaction System, by the Chemical Data Systems, Inc., Oxford, Pa. The reactor is a downflow tubular reactor having a length of 9 inches, an outside diameter of 3/8 inch, an inside diameter of 1/4 inch. In addition, the reactor is equipped with a 1/16 inch outside diameter, central-longitudinal thermowell. A feed stream comprising 74.5 volume percent helium, 24.5 volume percent oxygen and 1.0 volume percent 1-butene is charged to the reactor at a rate of 2.65 standard cubic feet (SCF) 1/hour. The Gas Hourly Space Velocity (GHSV) is 4,500 reciprocal hours and the catalyst bed temperature is 752° F. at atmospheric pressure. Analysis indicates that 65.30 percent of the butene is converted to 1,3 butadiene, with a selectivity of 91.80 percent and a yield of 59.95 percent.

EXAMPLE VI 1,3 butadiene is produced from butene by charging 1 ml (0.43 grams) of the catalyst of Example III to a continuous flow catalytic reaction system equipped with programmable gas chromatograph and marketed commercially under the tradename, Flow Diagram-S Chematic-CDS 800 CF-HP/GC catalytic reaction system, by the Chemical Data Sysems, Inc., Oxford, Pa. The reactor is a downflow tubular reactor having a length of 9 inches, an outside diameter of 93/8 inch, an inside diameter of 1/4 inch. In addition, the reactor was equipped with a 1/16 inch outside diameter, central-longitudinal thermowell. A feed stream comprising 74.5 volume percent helium, 24.5 volume oxygen and 1 volume percent 1-butene is charged to the reactor at a rate of 2.65 standard cubic feet (SCF)/hour. The Gas-Hourly Space Velocity (GHSV) is 4,500 reciprocal hours and the catalyst bed temperature is 752° F. at atmospheric pressure. Analysis indicates that 60.60 percent of the butene is converted to 1,3 butadiene, with a selectivity of 90.60 percent and a yield of 54.90 percent. EXAMPLE VII

1,3 butadiene is produced from butene by charging 1 ml (0.39 grams) of the catalyst of Example IV to a continuous flow catalytic reaction system equipped with programmable gas chromatograph and marketed commercially under the tradename, Flow Diagram-S Chematic-CDS 800 CF-HP/GC catalytic reaction system, by the Chemical Data Systems, Inc., Oxford, Pa. The reactor is a downflow tubular reactor having a length of 9 inches, an outside diameter of 3/8 inch, an inside diameter of 1/4 inch. In addition, the reactor is equipped with a 1/16 inch outside diameter, central-longitudinal thermowell. A feed stream comprising 74.5 volume percent helium, 24.5 volume percent oxygen and 1.0 volume percent 1-butene is charged to the reactor at a rate of 2.65 standard cubic feed (SCF)/hour. The Gas-Hourly Space Velocity (GHSV) is 4,500 reciprocal hours and the catalyst bed temperature is 797° F. at atmospheric pressure. Analysis indicates that 69.5 percent of the butene is converted to 1,3 butadiene, with a selectivity of 88.2 percent and a yield of 61.30 percent.

As can readily be determined from the above Examples, the dehydrogenation catalysts herein effectively convert mono-olefins, for example, 1-butene to diolefins such as, 1,3-butadiene under the described reaction conditions. Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims. 

We claim:
 1. A method for producing diolefins from monolefins which comprises reacting a feedstream comprising a gas containing helium, molecular oxygen and a C₄ and C₈ mono-olefin under reaction conditions, in contact with an oxidative dehydrogenation catalyst defined by the formula:

    Me.sub.a V.sub.b P.sub.c Sn.sub.d O.sub.e X

wherein X is mordenite, Me is an alkali metal, a is 0.10 to 2, b is 0.10 to 1, c is 1, d is 0.001 to 0.30 and e is a number which satisfies the valence requirements of the other elements present.
 2. The method defined in claim 1 wherein the alkali metal is a member selected from the group consisting of lithium, sodium, potassium, rubidium and cesium and mixtures thereof.
 3. The method defined in claim 1 wherein the feedstream comprises a gas containing helium, molecular oxygen and a C₄ to C₈ mono-olefin in a molar ratio of from 0.1:1:0.001 to 4:1:0.03.
 4. The method defined in claim 1 wherein the C₄ to C₈ mono-olefin is butene, pentene, cyclopentene, hexene, cyclohexene, heptene, cycloheptene, or octene or a mixture thereof.
 5. The method defined in claim 1 wherein the reaction conditions comprise a temperature from 500° F. to 760° F., a pressure of from atmospheric pressure to 200 p.s.i.g., and a gas hourly space velocity of from 2,400 to 6,000 reciprocal hours.
 6. A method for producing diolefins from mono-olefins which comprises reacting a feedstream comprising a gas containing helium, molecular oxygen and a C₄ to C₈ mono-olefin in the vapor phase, at a temperature of from 600° F. to 700° F., a pressure of from atmospheric pressure to 200 p.s.i.g., and a gas hourly space velocity of from 2,400 to 6,000 reciprocal hours in contact with an oxidative dehydrogenation catalyst described by the formula:

    Me.sub.a V.sub.b P.sub.c Sn.sub.d O.sub.e X

wherein X is mordenite, Me is an alkali metal, a is 0.1 to 2, b is 0.10 to 1, c is 1,d is 0.001 to 0.30 and e is a number which satisfies the valence requirements of the other elements present.
 7. The method defined in claim 6 wherein the alkali metal is a member selected from the group consisting of lithium, sodium, potassium, rubidium and cesium, and mixtures thereof.
 8. The method defined in claim 6 wherein the feedstream comprises a gas containing helium, molecular oxygen and a C₄ to C₈ mono-olefin in a molar ratio of from 0.1:1:0.001 to 4:1:0.03.
 9. The method defined in claim 6 wherein the C₄ to C₈ mono-olefin is butene, pentene, cyclopentene, hexene, cyclohexene, heptene, cycloheptene or octene or a mixture thereof.
 10. A method for producing 1,3-butadiene which comprises reacting a feedstream comprising helium, air and butene in a molar ratio of from 0.1:1:0.001 to 4:1:0.03 in the vapor phase at a temperature of from 600° F. to 700° F., a pressure of from atmospheric pressure to 200 p.s.i.g. and a gas hourly space velocity of from 2,400 to 6,000 reciprocal hours, in contact with a dehydrogenation catalyst described by the formula:

    K.sub.a V.sub.b P.sub.c Sn.sub.d O.sub.e X

wherein X is mordenite, a is 0.10 to 2, b is 0.10 to 1, c is 1, d is 0.001 to 0.30 and e is a number which satisfies the valence requirements of the other elements present.
 11. A method for producing diolefins from mono-olefins which comprises reacting a feedstream comprising a gas containing molecular oxygen and a C₄ to C₈ mono-olefin under reaction conditions, in contact with a catalyst defined by the formula:

    Me.sub.a V.sub.b P.sub.c Sn.sub.d O.sub.e X

wherein X is mordenite, Me is an alkali metal, a is 0.10 to 2, b is 0.10 to 1, C is 1, d is 0.001 to 0.30 and e is a number which satisfies the valence requirements of the other elements present.
 12. The method defined in claim 11 wherein the alkali metal is a member selected from the group consisting of lithium, sodium, potassium, rubidium and cesium and mixtures thereof.
 13. The method defined in claim 11 wherein the feedstream comprises a gas containing molecular oxygen and from about 0.1 to about 3 mole percent of a C₄ to C₈ mono-olefin.
 14. The method defined in claim 11 wherein the reaction conditions comprise a temperature of from about 500° F. to about 760° F., a pressure of from atmospheric pressure to about 200 p.s.i.g., and a gas hourly space velocity of from about 2,400 to about 6,000 reciprocal hours.
 15. The method defined in claim 11 wherein the C₄ to C₈ mono-olefin is butene, pentene, cyclopentene, hexene, cyclohexene, heptene, cycloheptene or octene or a mixture thereof.
 16. A method for producing diolefins from mono-olefins which comprises reacting a feedstream comprising a gas containing molecular oxygen and a C₄ to C₈ mono-olefin in the vapor phase at a temperature of from about 600° F. to about 700° F., a pressure of from atmospheric pressure to about 200 p.s.i.g., and a gas hourly space velocity of from about 2,400 to about 6,000 reciprocal hours in contact with an oxidative dehydrogenative catalyst described by the formula:

    Me.sub.a V.sub.b P.sub.c Sn.sub.d O.sub.e X

wherein X is mordenite, Me is an alkali metal, a is 0.1 to 2, b is 0.10 to 1, c is 1, d is 0.001 to 0.30 and e is a number which satisfies the valence requirements of the other elements present.
 17. The method defined in claim 16 wherein the alkali metal is a member selected from the group consisting of lithium, sodium, potassium, rubidium and cesium and mixtures thereof.
 18. The method defined in claim 16 wherein the feedstream comprises a gas containing molecular oxygen and from about 0.1 to about 3 mole percent of a C₄ to C₈ mono-olefin.
 19. The method defined in claim 18 wherein the C₄ to C₈ mono-olefin is butene, pentene, cyclopentene, hexene, cyclohexene, heptene, cycloheptene or octene or a mixture thereof.
 20. A method for producing diolefins which comprises contacting a C₄ to C₈ mono-olefin with a catalyst comprising an alkali metal, vanadium, phosphorus and mordenite.
 21. The method defined in claims 20 wherein the catalyst includes tin.
 22. The method defined in claim 20 including contacting the C₄ to C₈ mono-olefin with the catalyst in the presence of a gas containing molecular oxygen.
 23. A method for producing diolefins which comprises contacting a C₄ to C₈ mono-olefin with a catalyst comprising an alkali metal, vanadium, phosphorus, tin and mordenite.
 24. The method defined in claim 23 including contacting the C₄ to C₈ mono-olefin with the catalyst in the presence of a gas containing molecular oxygen.
 25. A method for producing diolefins which comprises reacting a feedstream comprising a gas containing molecular oxygen and C₄ to C₈ mono-olefin in the vapor phase at a temperature of from about 500° F. to about 760° F., a pressure of from atmospheric pressure to about 200 p.s.i.g. and a gas hourly space velocity of from about 2,400 to about 6,000 reciprocal hours, in contact with a catalyst comprising an alkali metal, vanadium, phosphorus and tin in combination with mordenite.
 26. The method defined in claim 25 wherein the C₄ to C₈ mono-olefin is butene, pentene, cyclopentene, hexene, cyclohexene, heptene, cycloheptene or octene or a mixture thereof.
 27. The method defined in claim 25 wherein the feedstream comprises a gas containing molecular oxygen and from 0.1 to about 3 mole percent of a C₄ to C₈ mono-olefin. 